Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly/idempotent/openWorld, so the safety profile is covered. The description adds genuine value beyond them: it discloses that the response contains a shareable planelec.be link reproducing the calculation, and that unset fields silently assume socket-circuit defaults rather than erroring. No limits, failure modes, or jurisdiction caveats (beyond 'Belgian AREI/RGIE') are mentioned.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, no filler. The first sentence front-loads what the tool computes and under which standard; the second tells the caller what to supply and what comes back. Every clause carries information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 13-parameter tool with zero required fields and an output schema, the description does the essential work: it tells the caller the minimal viable input and that an output link is returned. The gap is the undocumented 'check' mode branch, which changes what the tool returns and is only discoverable in the schema.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the baseline is 3, but the description adds practical meaning: it identifies the four inputs that actually drive a useful result and states that load may be expressed in A, W, kW or kVA, signalling that unit conversion is handled server-side. It does not clarify the mode/selectedCrossSectionMm2 interplay or the three-phase/3x-network constraint.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

Names a specific verb and resource ('Calculates the required copper or aluminium cable cross-section for a residential circuit under the Belgian AREI/RGIE') and enumerates the outputs (design current, voltage drop per cross-section, protection check, recommended cross-section). This is trivially distinguishable from the sibling tools (LED strip, inverter, regelwerk lookups).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Conveys the operating context (residential circuit, Belgian AREI) and tells the caller the minimal input set (load, length, network, breaker rating) while other fields fall back to socket-circuit defaults. However, it never explains the 'check' vs 'plan' modes or when to supply selectedCrossSectionMm2 — the most consequential usage decision — leaving that entirely to the schema.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.